dsh-table-attach: Drag or Paste Non-Image Files Directly in DSH Web Composer

The DSH web composer previously only supported pasting images. This plugin allows developers to drag and drop or paste non-image files, such as Excel, PDF, and CSV, directly into the editor. It saves files to the workspace and generates an `@reference` that the agent can read directly. It supports files under 50 MiB, blocks executable files, prevents path traversal, and supports both Chinese and English. The installation command is `dsh plugin add github:yybukn/dsh-table-attach`. It is mainly used to pass data files to an agent.